1. Field of the Invention
The present invention relates to an exothermic heat generating apparatus which is improved so as to enable repetition of stable exothermic reaction for long periods. For example, the exothermic heat generating apparatus is preferably used as a heat source for rapidly heating in a vehicle or the like. Further, in a cold starting time, the apparatus is used to heat a catalytic section, a cooling water section, an air intake section and the like to provide a substantial warm-up state at a time of engine start-up within a period of tens seconds. Alternatively, the apparatus is used as an auxiliary heat source for a power station. As one example, a description will hereinafter be given of an on-vehicle exothermic heat generating apparatus for use in a vehicle.
2. Description of the Related Art
Alkali earth oxides including MgO, CaO, SrO, and BaO react with water to generate hydroxides, respectively. Heating can decompose the hydroxides to generate the original oxides while releasing the water. The hydroxides including Mg(OH).sub.2, Ca(OH).sub.2, Sr(OH).sub.2, and Ba(OH).sub.2 are said to have respective decomposition temperatures of 260.degree. C., 480.degree. C., 580.degree. C., and 730.degree. C. Therefore, it is basically possible to establish a reversible cycle by using any one of the alkali earth oxides.
Further, since the respective hydroxides have the inherent decomposition temperatures, it is also possible to mix the oxides at desired rates so as to prepare a range of the decomposition temperatures according to a range of obtained regeneration temperatures in some applications. For example, regeneration at lower temperatures can be realized by mixing MgO and CaO.
As an example, a description will now be given of calcium oxide. It is known that the calcium oxide reacts with splashed water to rapidly generate exothermic heat reaching the maximum temperature of about 400.degree. C. In reality, this exothermic reaction is widely put to practical use for one-time heating purpose in sake, a lunch box, or the like. When the water is used, a calorific value is 65.9 KJ (i.e., 213 cal/g in total weight including CaO and H.sub.2 O). When water vapor is used, the calorific value is 109.3 KJ (i.e., 352 cal/g) because evaporation heat of water is added. However, it is difficult to put a water vapor system to practical use since the water vapor system requires a pressure-proof container.
The exothermic reaction can be applied to a vehicle as disclosed in Japanese Patent Publications (Kokai) Nos. 59-208118 and 5-141228. In the above patents, calcium oxide particles are preset in a catalytic section of the vehicle, and water is introduced through another passage into the catalytic section at a time of engine start-up to cause the exothermic reaction. Further, decomposition reaction is also caused to provide the original calcium oxide during travelling.
However, the exothermic heat generating apparatus disclosed in the above cited references can not exhibit its performance for long terms due to the following reasons. This is because these apparatus employ open systems, and their effects are inevitably deteriorated due to a carbon dioxide gas in air. That is, after the calcium oxide is changed into the calcium hydroxide, the heating can easily return the calcium hydroxide to the calcium oxide in an earlier period. However, the calcium hydroxide may be left as it is for a long time since, for example, the vehicle is left overnight. In such a case, the calcium hydroxide gradually sucks in the carbon dioxide gas in the air through an exhaust vent of a silencer, and is changed into calcium carbonate. The calcium carbonate can not be easily decomposed due to its high decomposition temperature of 840.degree. C. As a result, an amount of the calcium oxide serving as reactant is gradually reduced. After a week, 100% calcium carbonate is generated, resulting in complete loss of an initially designed performance.
FIG. 1 is a graph showing a rate of deterioration of the calcium oxide in the air by using as indexes an increase in weight of the calcium oxide left in dry nitrogen or in moist nitrogen. The ordinate axis defines an increased amount of weight (percent), and the transverse axis defines a time (min). The characteristic curve a shows an increased amount of weight of calcium oxide powder left in the moist nitrogen, and the characteristic curve b shows an increased amount of weight of a calcium oxide press molded product in the moist nitrogen. Further, the characteristic curve c shows an increased amount of weight of the calcium oxide powder in the dry nitrogen, and the characteristic curve d shows an increased amount of weight of the calcium oxide press molded product in the dry nitrogen. It can be understood from the drawing that the rate of deterioration in the moist nitrogen is four times faster than that in the dry nitrogen. The result is natural since the calcium oxide can react with moisture.
FIG. 2 shows an infrared absorption spectrum of samples (of the calcium oxide powder) which are left in the air for one night and day. It is apparent that a tremendously large amount of carbonation is generated though the carbon dioxide gas concentration in the air is only 0.003%. This is because the generating calcium hydroxide can easily react with the carbon dioxide gas.
The conventional exothermic heat generating apparatus employs the open system using the reversible reaction between the alkali earth oxide and the water. As a result, there are problems in that its effect is inevitably deteriorated due to the carbon dioxide gas in the air, and can not be exhibited for long terms.